Method for purifying dianhydrides

ABSTRACT

A method for purifying dianhydrides is provided. In one aspect, purified oxybisphthalic anhydrides, intermediates useful in the preparation of polyetherimides are provided. In one embodiment, a first solution containing a dianhydride compound, a solvent, and a phase transfer catalyst is contacted with a solid inorganic adsorbent material having a total pore volume of about 0.5 milliliters/gram or greater and a cumulative pore volume distribution of about 20 percent or greater of particles having a pore diameter in a range between about 3 nanometers and about 20 nanometers. The solution containing the dianhydride compound is then separated from the solid inorganic adsorbent material to provide a purified dianhydride compound which is substantially free of the phase transfer catalyst. The purification technique is especially valuable for preparing high purity oxybisphthalic anhydrides, such as 4,4′-oxybisphthalic anhydride (4,4′-ODPA), which are substantially free of residual phase transfer catalyst.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of U.S. patent applicationSer. No. 11/603,764 filed Nov. 22, 2006, now U.S. Pat. No. 7,446,214,which is a Continuation-In-Part of U.S. patent application Ser. No.11/234,022 entitled “Method for Purifying Oxybisphthalic Compounds”,filed Sep. 23, 2005, now abandoned.

BACKGROUND

The invention relates generally to the purification of dianhydrides andrelated bisimides. In one aspect the invention relates to thepurification of dianhydrides and bisimides which are oxybisphthaliccompounds. In a particular aspect, the invention relates to thepurification of oxybisphthalic anhydrides.

Oxybisphthalic compounds, such as for example, oxybisphthalic anhydride(ODPA) are key raw materials used in preparation of polyetherimides.Bisimides related to ODPA, for example the N,N′-dimethylbisimide ofODPA, are useful intermediates in ODPA preparation. ODPA itself is a keymonomer useful in the preparation of high temperature polyetherimides bycondensation polymerization reaction with a diamine. In general,condensation polymerization processes require that the componentmonomers be of high purity in order to effectively build polymermolecular weight, obtain good reaction kinetics, and provide a thermallystable and processable polymer.

ODPA can be produced by the phase transfer catalyzed coupling ofchlorophthalic anhydride in the presence of potassium carbonate and anorganic phase transfer catalyst, such as hexaethylguanidinium chloride(HEGCl). Alternately, ODPA can be produced by hydrolysis of the relatedbisimide prepared in turn by phase transfer catalyzed coupling of anN-alkyl chlorophthalimide in the presence of potassium carbonate and anorganic phase transfer catalyst, such as hexaethylguanidinium chloride(HEGCl). Although the coupling processes are efficient in the presenceof the organic phase transfer catalyst, the product dianhydride orrelated bisimide may contain a significant fraction of the phasetransfer catalyst employed, or its reaction and/or degradationproducts/adducts. Residual phase transfer catalyst has been shown tohave an adverse effect on the thermal stability of polymers preparedusing ODPA as a monomer or comonomer.

Therefore, there is a need for dianhydrides and related bisimides whichare substantially free of residual phase transfer catalyst. Moreover,there is a need for more efficient methods for the separation ofresidual organic phase transfer catalysts from dianhydrides and relatedbisimides prepared using synthetic methods involving one or morereactions mediated by a phase transfer catalyst.

BRIEF DESCRIPTION

In one embodiment, the present invention provides a method of purifyinga dianhydride, said method comprising the steps of:

(a) providing a first solution comprising at least one dianhydride, atleast one solvent, and at least one organic phase transfer catalyst; and

(b) contacting the first solution with a solid inorganic adsorbentmaterial, said solid inorganic adsorbent material having a total porevolume of about 0.5 milliliters/gram or greater, and a cumulative porevolume distribution of about 20 percent or greater of particles having apore diameter in a range between about 3 nanometers and about 20nanometers; to provide a second solution of the dianhydride, which issubstantially free of the organic phase transfer catalyst.

In another aspect, the present invention provides a method for purifyingan oxybisphthalic anhydride having structure (IV),

The method comprises steps (a) and (b). In step (a), a first solutioncomprising at least one oxybisphthalic anhydride (IV), at least onesolvent, and at least one organic phase transfer catalyst is provided.In step (b), the first solution is contacted with a solid inorganicadsorbent material, said solid inorganic adsorbent material having atotal pore volume of about 0.5 milliliters/gram or greater, and acumulative pore volume distribution of about 20 percent or greater ofparticles having a pore diameter in a range between about 3 nanometersand about 20 nanometers; to provide a second solution of theoxybisphthalic anhydride (IV), which is substantially free of the phasetransfer catalyst.

In yet another aspect, the present invention provides a method forpurifying an oxybisphthalic anhydride having structure (IV), the methodcomprising the steps of:

(a) providing a first solution comprising at least one oxybisphthalicanhydride (IV), ortho-dichlorobenzene solvent, and ahexaalkylguanidinium halide phase transfer catalyst; and

(b) contacting the first solution with a silica, said silica havinghaving a total pore volume of about 0.5 milliliters/gram or greater, anda cumulative pore volume distribution of about 20 percent or greater ofparticles having a pore diameter in a range between about 3 nanometersand about 20 nanometers; said contacting being carried out at atemperature in a range between about 50° C. and about 250° C. to providea second solution of the oxybisphthalic anhydride (IV) which issubstantially free of said phase transfer catalyst.

In a still another aspect, the present invention provides a method forpreparing an oxybisphthalic anhydride having structure (IV). The methodcomprises steps (a)-(e). In step (a), at least one inorganic carbonatesalt, at least one organic phase transfer catalyst, and at least onesubstituted phthalic compound having structure (VI),

wherein Z is oxygen; and X¹ is independently selected from the groupconsisting of fluoro, chloro, bromo, iodo, and nitro groups; arecontacted to provide a first product mixture comprising the at least oneorganic phase transfer catalyst and the oxybisphthalic anhydride (IV).In Step (b) the first product mixture is diluted with at least onesolvent to provide a second product mixture comprising the at least oneorganic phase transfer catalyst and the oxybisphthalic anhydride (IV).In step (c), substantially all of the oxybisphthalic anhydride (IV)present in the second product mixture is dissolved to provide a thirdproduct mixture, said third product mixture comprising less than 25 ppmwater, and wherein said oxybisphthalic anhydride (IV) is present in anamount corresponding to less than 25 percent by weight of a total weightof the third product mixture. In step (d), the third product mixture isfiltered at a temperature above the crystallization point temperature ofthe oxybisphthalic anhydride (IV) to provide a first solution of theoxybisphthalic anhydride (IV). In step (e), the first solution iscontacted with a silica, said silica having a total pore volume of about0.5 milliliters/gram or greater, and a cumulative pore volumedistribution of about 20 percent or greater of particles having a porediameter in a range between about 3 nanometers and about 20 nanometers;said contacting being carried out at a temperature in a range betweenabout 50° C. and about 250° C. to provide a second solution of theoxybisphthalic anhydride (IV), which is substantially free of said phasetransfer catalyst.

In other aspects, the present invention provides a purifiedoxybisphthalic anhydride having structure (IV) comprising less thanabout 150 parts per million of an organic phase transfer catalyst. Thepurified oxybisphthalic anhydrides provided by the present invention areuseful in the preparation of polyetherimides.

These and other features, aspects, and advantages of the presentinvention may be more understood more readily by reference to thefollowing detailed description.

DETAILED DESCRIPTION

In the following specification and the claims which follow, referencewill be made to a number of terms which shall be defined to have thefollowing meanings:

The singular forms “a”, “an” and “the” include plural referents unlessthe context clearly dictates otherwise.

“Optional” or “optionally” means that the subsequently described eventor circumstance may or may not occur, and that the description includesinstances where the event occurs and instances where it does not.

As used herein, the term “aromatic radical” refers to an array of atomshaving a valence of at least one comprising at least one aromatic group.The array of atoms having a valence of at least one comprising at leastone aromatic group may include heteroatoms such as nitrogen, sulfur,selenium, silicon and oxygen, or may be composed exclusively of carbonand hydrogen. As used herein, the term “aromatic radical” includes butis not limited to phenyl, pyridyl, furanyl, thienyl, naphthyl,phenylene, and biphenyl radicals. As noted, the aromatic radicalcontains at least one aromatic group. The aromatic group is invariably acyclic structure having 4 n+2 “delocalized” electrons where “n” is aninteger equal to 1 or greater, as illustrated by phenyl groups (n=1),thienyl groups (n=1), furanyl groups (n=1), naphthyl groups (n=2),azulenyl groups (n=2), anthracenyl groups (n=3) and the like. Thearomatic radical may also include nonaromatic components. For example, abenzyl group is an aromatic radical which comprises a phenyl ring (thearomatic group) and a methylene group (the nonaromatic component).Similarly a tetrahydronaphthyl radical is an aromatic radical comprisingan aromatic group (C₆H₃) fused to a nonaromatic component —(CH₂)₄—. Forconvenience, the term “aromatic radical” is defined herein to encompassa wide range of functional groups such as alkyl groups, alkenyl groups,alkynyl groups, haloalkyl groups, haloaromatic groups, conjugated dienylgroups, alcohol groups, ether groups, aldehyde groups, ketone groups,carboxylic acid groups, acyl groups (for example carboxylic acidderivatives such as esters and amides), amine groups, nitro groups, andthe like. For example, the 4-methylphenyl radical is a C₇ aromaticradical comprising a methyl group, the methyl group being a functionalgroup which is an alkyl group. Similarly, the 2-nitrophenyl group is aC₆ aromatic radical comprising a nitro group, the nitro group being afunctional group. Aromatic radicals include halogenated aromaticradicals such as 4-trifluoromethylphenyl,hexafluoroisopropylidenebis(4-phen-1-yloxy) (i.e., —OPhC(CF₃)₂PhO—),4-chloromethylphen-1-yl, 3-trifluorovinyl-2-thienyl,3-trichloromethylphen-1-yl (i.e., 3-CCl₃Ph-),4-(3-bromoprop-1-yl)phen-1-yl (i.e., 4-BrCH₂CH₂CH₂Ph-), and the like.Further examples of aromatic radicals include 4-allyloxyphen-1-oxy,4-aminophen-1-yl (i.e., 4-H₂NPh-), 3-aminocarbonylphen-1-yl (i.e.,NH₂COPh-), 4-benzoylphen-1-yl, dicyanomethylidenebis(4-phen-1-yloxy)(i.e., —OPhC(CN)₂PhO—), 3-methylphen-1-yl, methylenebis(4-phen-1-yloxy)(i.e., —OPhCH₂PhO—), 2-ethylphen-1-yl, phenylethenyl,3-formyl-2-thienyl, 2-hexyl-5-furanyl,hexamethylene-1,6-bis(4-phen-1-yloxy) (i.e., —OPh(CH₂)₆PhO—),4-hydroxymethylphen-1-yl (i.e., 4-HOCH₂Ph-), 4-mercaptomethylphen-1-yl(i.e., 4-HSCH₂Ph-), 4-methylthiophen-1-yl (i.e., 4-CH₃SPh-),3-methoxyphen-1-yl, 2-methoxycarbonylphen-1-yloxy (e.g., methylsalicyl), 2-nitromethylphen-1-yl (i.e., 2-NO₂CH₂Ph),3-trimethylsilylphen-1-yl, 4-t-butyldimethylsilylphenl-1-yl,4-vinylphen-1-yl, vinylidenebis(phenyl), and the like. The term “aC₃-C₁₀ aromatic radical” includes aromatic radicals containing at leastthree but no more than 10 carbon atoms. The aromatic radical1-imidazolyl (C₃H₂N₂—) represents a C₃ aromatic radical. The benzylradical (C₇H₇—) represents a C₇ aromatic radical.

As used herein the term “cycloaliphatic radical” refers to a radicalhaving a valence of at least one, and comprising an array of atoms whichis cyclic but which is not aromatic. As defined herein a “cycloaliphaticradical” does not contain an aromatic group. A “cycloaliphatic radical”may comprise one or more noncyclic components. For example, acyclohexylmethyl group (C₆H₁₁CH₂—) is a cycloaliphatic radical whichcomprises a cyclohexyl ring (the array of atoms which is cyclic butwhich is not aromatic) and a methylene group (the noncyclic component).The cycloaliphatic radical may include heteroatoms such as nitrogen,sulfur, selenium, silicon and oxygen, or may be composed exclusively ofcarbon and hydrogen. For convenience, the term “cycloaliphatic radical”is defined herein to encompass a wide range of functional groups such asalkyl groups, alkenyl groups, alkynyl groups, haloalkyl groups,conjugated dienyl groups, alcohol groups, ether groups, aldehyde groups,ketone groups, carboxylic acid groups, acyl groups (for examplecarboxylic acid derivatives such as esters and amides), amine groups,nitro groups, and the like. For example, the 4-methylcyclopent-1-ylradical is a C₆ cycloaliphatic radical comprising a methyl group, themethyl group being a functional group which is an alkyl group.Similarly, the 2-nitrocyclobut-1-yl radical is a C₄ cycloaliphaticradical comprising a nitro group, the nitro group being a functionalgroup. A cycloaliphatic radical may comprise one or more halogen atomswhich may be the same or different. Halogen atoms include, for example;fluorine, chlorine, bromine, and iodine. Cycloaliphatic radicalscomprising one or more halogen atoms include2-trifluoromethylcyclohex-1-yl, 4-bromodifluoromethylcyclooct-1-yl,2-chlorodifluoromethylcyclohex-1-yl,hexafluoroisopropylidene-2,2-bis(cyclohex-4-yl) (i.e.,—C₆H₁₀C(CF₃)₂C₆H₁₀—), 2-chloromethylcyclohex-1-yl,3-difluoromethylenecyclohex-1-yl, 4-trichloromethylcyclohex-1-yloxy,4-bromodichloromethylcyclohex-1-ylthio, 2-bromoethylcyclopent-1-yl,2-bromopropylcyclohex-1-yloxy (e.g., CH₃CHBrCH₂C₆H₁₀O—), and the like.Further examples of cycloaliphatic radicals include4-allyloxycyclohex-1-yl, 4-aminocyclohex-1-yl (i.e., H₂C₆H₁₀—),4-aminocarbonylcyclopent-1-yl (i.e., NH₂COC₅H₈—),4-acetyloxycyclohex-1-yl, 2,2-dicyanoisopropylidenebis(cyclohex-4-yloxy)(i.e., —OC₆H₁₀C(CN)₂C₆H₁₀O—), 3-methylcyclohex-1-yl,methylenebis(cyclohex-4-yloxy) (i.e., —OC₆H₁₀CH₂C₆H₁₀O—),1-ethylcyclobut-1-yl, cyclopropylethynyl, 3-formyl-2-tetrahydrofuranyl,2-hexyl-5-tetrahydrofuranyl, hexamethylene-1,6-bis(cyclohex-4-yloxy)(i.e., —OC₆H₁₀(CH₂)₆C₆H₁₀O—), 4-hydroxymethylcyclohex-1-yl (i.e.,4-HOCH₂C₆H₁₀—), 4-mercaptomethylcyclohex-1-yl (i.e., 4-HSCH₂C₆H₁₀—),4-methylthiocyclohex-1-yl (i.e., 4-CH₃SC₆H₁₀—), 4-methoxycyclohex-1-yl,2-methoxycarbonylcyclohex-1-yloxy (2-CH₃OCOC₆H₁₀O—),4-nitromethylcyclohex-1-yl (i.e., NO₂CH₂C₆H₁₀—),3-trimethylsilylcyclohex-1-yl, 2-t-butyldimethylsilylcyclopent-1-yl,4-trimethoxysilylethylcyclohex-1-yl (e.g., (CH₃O)₃SiCH₂CH₂C₆H₁₀—),4-vinylcyclohexen-1-yl, vinylidenebis(cyclohexyl), and the like. Theterm “a C₃-C₁₀ cycloaliphatic radical” includes cycloaliphatic radicalscontaining at least three but no more than 10 carbon atoms. Thecycloaliphatic radical 2-tetrahydrofuranyl (C₄H₇O—) represents a C₄cycloaliphatic radical. The cyclohexylmethyl radical (C₆H₁₁CH₂—)represents a C₇ cycloaliphatic radical.

As used herein the term “aliphatic radical” refers to an organic radicalhaving a valence of at least one consisting of a linear or branchedarray of atoms which is not cyclic. Aliphatic radicals are defined tocomprise at least one carbon atom. The array of atoms comprising thealiphatic radical may include heteroatoms such as nitrogen, sulfur,silicon, selenium and oxygen or may be composed exclusively of carbonand hydrogen. For convenience, the term “aliphatic radical” is definedherein to encompass, as part of the “linear or branched array of atomswhich is not cyclic” a wide range of functional groups such as alkylgroups, alkenyl groups, alkynyl groups, haloalkyl groups, conjugateddienyl groups, alcohol groups, ether groups, aldehyde groups, ketonegroups, carboxylic acid groups, acyl groups (for example carboxylic acidderivatives such as esters and amides), amine groups, nitro groups, andthe like. For example, the 4-methylpent-1-yl radical is a C₆ aliphaticradical comprising a methyl group, the methyl group being a functionalgroup which is an alkyl group. Similarly, the 4-nitrobut-1-yl group is aC₄ aliphatic radical comprising a nitro group, the nitro group being afunctional group. An aliphatic radical may be a haloalkyl group whichcomprises one or more halogen atoms which may be the same or different.Halogen atoms include, for example; fluorine, chlorine, bromine, andiodine. Aliphatic radicals comprising one or more halogen atoms includethe alkyl halides trifluoromethyl, bromodifluoromethyl,chlorodifluoromethyl, hexafluoroisopropylidene, chloromethyl,difluorovinylidene, trichloromethyl, bromodichloromethyl, bromoethyl,2-bromotrimethylene (e.g., —CH₂CHBrCH₂—), and the like. Further examplesof aliphatic radicals include allyl, aminocarbonyl (i.e., —CONH₂),carbonyl, 2,2-dicyanoisopropylidene (i.e., —CH₂C(CN)₂CH₂—), methyl(i.e., —CH₃), methylene (i.e., —CH₂—), ethyl, ethylene, formyl (i.e.,—CHO), hexyl, hexamethylene, hydroxymethyl (i.e., —CH₂OH),mercaptomethyl (i.e., —CH₂SH), methylthio (i.e., —SCH₃),methylthiomethyl (i.e., —CH₂SCH₃), methoxy, methoxycarbonyl (i.e.,CH₃OCO—), nitromethyl (i.e., —CH₂NO₂), thiocarbonyl, trimethylsilyl(i.e., (CH₃)₃Si—), t-butyldimethylsilyl, 3-trimethoxysilylpropyl (i.e.,(CH₃O)₃SiCH₂CH₂CH₂—), vinyl, vinylidene, and the like. By way of furtherexample, a C₁-C₁₀ aliphatic radical contains at least one but no morethan 10 carbon atoms. A methyl group (i.e., CH₃—) is an example of a C₁aliphatic radical. A decyl group (i.e., CH₃(CH₂)₉—) is an example of aC₁₀ aliphatic radical.

The present invention provides new and useful methodology for thepurification of dianhydrides and related bisimides. It is believed thatalmost any dianhydride or related bisimide containing one or moreorganic phase transfer catalysts may be purified efficiently using themethod of the present invention. By purified, it is meant that thedianhydride and/or the related bisimide may be separated from the phasetransfer catalyst contaminant in such a manner such that the purifieddianhydride and/or the related bisimide is substantially free ofresidual phase transfer catalyst.

While it is believed that the methods developed here are generallyapplicable to the purification of dianhydrides and related bisimides,the methods have been demonstrated to be especially effective in theremoval of organic phase transfer catalysts from oxybisphthalicanhydrides and oxybisphthalimides, collectively referred to herein attimes as oxybisphthalic compounds. Thus, in one embodiment, the presentinvention provides a method for purifying an oxybisphthalic compoundhaving structure (I),

wherein Z is independently at each occurrence O or N—R¹, and R¹ is aC₁-C₈ aliphatic radical, a C₃-C₁₂ cycloaliphatic radical, or a C₃-C₁₂aromatic radical; said method comprising the steps of:(a) providing a first solution comprising at least one oxybisphthaliccompound having structure (I), at least one solvent, and at least oneorganic phase transfer catalyst; and(b) contacting the first solution with a solid inorganic adsorbentmaterial, said solid inorganic adsorbent material having a total porevolume of about 0.5 milliliters/gram or greater, and a cumulative porevolume distribution of about 20 percent or greater of particles having apore diameter in a range between about 3 nanometers and about 20nanometers; to provide a second solution of the oxybisphthalic compoundhaving structure (I), which is substantially free of the organic phasetransfer catalyst.

The term “providing a first solution comprising at least oneoxybisphthalic compound having structure (I), at least one solvent, andat least one organic phase transfer catalyst” refers to any process bywhich the first solution comprising the oxybisphthalic compound, thesolvent, and the organic phase transfer catalyst can be provided.Moreover, the scope of the term includes all the various methods bywhich the oxybisphthalic compound can be prepared. In an embodiment, thefirst solution is provided by dissolving a solid mixture comprising anoxybisphthalic compound and at least one organic phase transfer catalystin at least one solvent. In another embodiment, the first solution isprovided by reacting a halophthalic anhydride with potassium carbonatein a solvent, in the presence of at least one organic phase transfercatalyst to provide a mixture comprising an oxybisphthalic anhydride,potassium chloride, and said at least one phase transfer catalyst; andfiltering said mixture to provide a first solution.

Non-limiting examples of oxybisphthalic compounds (I) includeoxybisphthalimides having structure (II)

wherein R¹ is a C₁-C₈ aliphatic radical, a C₃-C₁₂ cycloaliphaticradical, or a C₃-C₁₂ aromatic radical. Non-limiting examples of suchoxybisphthalimides having structure (II) include4,4′-oxybis(N-methylpthalimide) (CAS No. 27507-54-6);3,4′-oxybis(N-ethylphthalimide); 4,4′-oxybis(N-propylphthalimide);3,3′-oxybis(N-butylphthalimide); 4,4′-oxybis(N-phenylphthalimide);4,4′-oxybis[N-(ortho-tolyl)phthalimide];4,4′-oxybis(N-benzylphthalimide); 4,4′-oxybis(N-cyclopentylphthalimide);3,4′-oxybis(N-cyclohexylphthalimide); and the like.

In a particular embodiment, the oxybisphthalic compound comprises4,4′-oxybisphthalimide (III),

wherein R¹ is a C₁-C₈ aliphatic radical, a C₃-C₁₂ cycloaliphaticradical, or a C₃-C₁₂ aromatic radical. The oxybisphthalimides are usefulin the preparation the corresponding oxybisphthalic anhydrides, which inturn are as precursors to the corresponding dianhydrides which areuseful for preparing polyetherimides.

In one embodiment, the oxybisphthalic compound which can be purified bythe method of the present invention is an oxybisphthalic anhydridehaving structure (IV).

Oxybisphthalic anhydride is hereinafter sometimes also referred to bythe abbreviation “ODPA”. Structure (IV) refers to the 3,4′-ODPA;4,4′-ODPA; and 3,3′-ODPA isomers either singly or as mixtures containingtwo or more of 3,4′-ODPA; 4,4′-ODPA; and 3,3′-ODPA isomers. Each of thegeneric groups represented by generic structures I, II, and IV includespure compounds as well as mixtures of compounds. For example, genericstructure I may be used to represent a pure compoundN,N′-di-t-butyl-4,4′-oxybisphthalimide. Alternately, generic structure Imay be used to represent a mixture comprisingN,N′-di-t-butyl-4,4′-oxybisphthalimide,N,N′-di-t-butyl-3,4′-oxybisphthalimide andN,N′-di-t-butyl-3,3′-oxybisphthalimide. Similarly, oxybisphthalicanhydride structure IV may be used to represent a single dianhydride,for example pure 4,4′-oxybisphthalic anhydride. Alternately genericstructure IV may be used to represent a mixture comprising4,4′-oxybisphthalic anhydride, 3,4′-oxybisphthalic anhydride, and3,3′-oxybisphthalic anhydride. In one embodiment, structure IVrepresents an oxybisphthalic anhydride consisting essentially of3,3′-oxybisphthalic anhydride. In an alternate embodiment, structure IVrepresents an oxybisphthalic anhydride consisting essentially of3,4′-oxybisphthalic anhydride. In yet another embodiment, structure IVrepresents a mixture of 3,3′-oxybisphthalic anhydride and3,4′-oxybisphthalic anhydride. In alternate embodiments, minor amounts(i.e., each of the “minor” components represents less than about lessthan about 5 percent by weight of the total weight of the composition)of the 3,3′-oxybisphthalic anhydride and 3,4′-oxybisphthalic anhydrideare present in an oxybisphthalic anhydride consisting primarily of4,4′-oxybisphthalic anhydride. In yet another embodiment, structure IVrepresents a oxybisphthalic anhydride isomer mixture consisting of about49 percent by weight 4,4′-ODPA, about 42 percent by weight of 3,4′-ODPAand about 9 percent by weight of 3,3′-ODPA. In one embodiment, theoxybisphthalic anhydride represented as structure IV consists primarilyof 4,4′-oxybisphthalic anhydride, a dianhydride having structure (V). Asused herein, the term “consisting primarily of” refers to a compositionhaving a major component that represents 90 percent by weight or more ofthe total weight of the composition.

Compounds I-V can be prepared by methods known in the art, for exampleby reaction of a substituted phthalic compound VI,

wherein “Z” is O or N—R¹, wherein R¹ is a C₁-C₈ aliphatic radical, aC₃-C₁₂ cycloaliphatic radical, or a C₃-C₁₂ aromatic radical; and X¹ isselected from the group consisting of fluoro, chloro, bromo, iodo, andnitro groups; with at least one inorganic carbonate salt, in at leastone solvent, in the presence of at least one organic phase transfercatalyst. Aprotic solvents are generally used. Examples of solventsinclude chlorobenzene, ortho-dichlorobenzene, para-dichlorobenzene,dichlorotoluene, 1,2,4-trichlorobenzene, diphenyl sulfone, phenetole,anisole, veratrole, toluene, xylene, mesitylene, or mixtures thereof.The reaction provides a first product mixture comprising at least oneoxybisphthalic compound I, an inorganic salt by-product, and the organicphase transfer catalyst. The reaction is typically carried out byheating the reactants and solvent in a stirred reactor. In oneembodiment, the reaction mixture is heated to a temperature in a rangefrom about 50° C. to about 250° C. The reactor can be equipped with ameans for removing solvent by distillation, such as a distillation head,condenser, and receiver. Solvent may be distilled from the reactionmixture during the reaction or upon its completion as a means forremoving adventitious water or water produced during the reaction. Theproduct mixture typically comprises less than about 100 ppm of water aswell. The identity of the salt by-product is determined by the inorganiccarbonate employed as well as the nature of the substituent leavinggroup in the substituted phthalic anhydride (X¹ in structure VI). Forexample, when the substituted phthalic anhydride is 4-nitrophthalicanhydride and the inorganic carbonate is sodium carbonate, the saltby-product is sodium nitrite. As a further example, when the substitutedphthalic anhydride is 4-chlorophthalic anhydride and the inorganiccarbonate is potassium carbonate, the salt by-product is potassiumchloride.

Suitable substituted phthalic compounds embraced by structure VI includesubstituted phthalimides and phthalic anhydrides. In one embodiment, asubstituted phthalimide having structure VI wherein Z=NR¹, is used.Examples of suitable substituted phthalimides include substitutedN-alkylphthalimides, substituted N-arylphthalimides, and substitutedN-cycloalkylphthalimides, comprising a chlorine, fluorine, bromine,iodine, or nitro group in the 3- or the 4-position. These compounds canbe prepared by reacting an aliphatic, aromatic, or cycloaliphaticprimary amine with a phthalic anhydride substituted with a chlorine,fluorine, bromine, iodine, or nitro group in the 3- or the 4-position.Some examples of substituted phthalic anhydrides include,3-chlorophthalic anhydride, 4-chlorophthalic anhydride, 3-fluorophthalicanhydride, 4-fluorophthalic anhydride, 4-nitrophthalic anhydride,3-nitrophthalic anhydride, and mixtures thereof. Chlorophthaliccompounds are frequently used since they are easily prepared fromreadily available starting materials. Alkali metal carbonates arecommonly used as the inorganic carbonate salt. For example, 4,4′-ODPAcan be produced by the coupling of 4-chlorophthalic anhydride usingpotassium carbonate as the inorganic carbonate salt and an organic phasetransfer catalyst, for example a hexaalkylguanidinium halide salt suchas hexaethylguanidinium chloride (HEGCl). The inorganic by-product undersuch conditions is the corresponding alkali metal chloride.

Organic phase transfer catalysts (PTC's) are known in the art. Referenceis made, for example, to U.S. Pat. No. 5,081,298. Typical phase transfercatalysts include hexaalkylguanidinium salts, pyridinium salts,phosphazenium salts and the like. Representative hexaalkylguanidiniumsalts are illustrated by formula (VII). Representative pyridinium saltsare illustrated by formula (VIII). Representative phosphazeniumcatalysts are illustrated by formula (IX).

In structures (VII), (VIII) and (IX), the groups R²-R¹² areindependently a C₁-C₂₀ aliphatic radical, a C₃-C₄₀ aromatic radical, ora C₃-C₂₀ cycloaliphatic radical; and X⁻ is a monovalent inorganic anion,a monovalent organic anion, a polyvalent inorganic anion, a polyvalentorganic anion, or a mixture thereof. With respect to structure (IX), “p”is 0 or an integer from 1 to 10. In structures (VII), (VIII) and (IX),two or more of the groups represented by R²-R¹², when present in thesame structure, may be linked together to form a cyclic structurecomprising at least one nitrogen atom. Suitable organic phase transfercatalysts having general structure (VII) are illustrated byhexaethylguanidinium mesylate, hexaethylguanidinium chloride,hexaethylguanidinium bromide, hexaethylguanidinium acetate, andcombinations thereof. Suitable organic phase transfer catalysts havinggeneral structure (VIII) are illustrated by1-neopentyl-4-(N,N-dibutylamino)-pyridinium chloride;1-neopentyl-4-piperidin-1-ylpyridinium chloride;1-neopentyl-4-piperidin-1-ylpyridinium mesylate;1-3-methylheptyl-4-(4-methyl)-piperidin-1-ylpyridinium chloride, andcombinations thereof. Suitable organic phase transfer catalysts havinggeneral structure (IX) are illustrated by octamethylphosphazeniumchloride (p=0), octamethylphosphazenium bromide (p=0),dodecamethylphosphazenium chloride (p=1), dodecamethylphosphazeniummesylate (p=1), and mixtures thereof. The amount of organic phasetransfer catalyst is typically used in an amount corresponding to fromabout 0.1 mole percent to about 10 mole percent based on the totalnumber of moles of substituted phthalic anhydride employed.

In one embodiment, the organic phase transfer catalyst is abisguanidinium salt having structure (X)

wherein each of R¹³, R¹⁴, R¹⁵, R¹⁶, R¹⁷ and R¹⁸ is independently C₁-C₂₀aliphatic radical, a C₃-C₄₀ aromatic radical, or a C₃-C₂₀ cycloaliphaticradical. In addition two or more of R¹², R¹³, R¹⁴, R¹⁵, R¹⁶ and R¹⁷ maytogether form a cycloaliphatic radical or an aromatic radical comprisingat least one nitrogen atom. The anionic species, X⁻ (at times hereinreferred to as the “counterion”), represents one or more monovalentinorganic anions, monovalent organic anions, polyvalent inorganicanions, polyvalent organic anions, and mixtures thereof. Suitableorganic phase transfer catalysts having structure (X) include thebisguanidinium salt wherein R¹³, R¹⁴, R¹⁵, R¹⁶, and R¹⁷ are methylgroups, R¹⁸ is a 1,3-propanediyl radical (i.e., —CH₂CH₂CH₂—), and X⁻represents two chloride anions.

In one embodiment, the inorganic carbonate salt has a structure (XI)

wherein M is a metal ion selected from the group consisting of alkalimetal ions, alkaline earth metal ions, and mixtures thereof, and Y is OMor OH. In one embodiment the metal ion M is lithium, sodium, potassium,or a mixture thereof. Suitable inorganic carbonates include potassiumcarbonate, sodium carbonate, potassium sodium carbonate, lithiumcarbonate, potassium lithium carbonate, sodium lithium carbonate,potassium bicarbonate, sodium bicarbonate, lithium bicarbonate, andmixtures thereof.

Typically, the inorganic carbonate and the substituted phthalic compound(VI) are employed in amounts corresponding to a ratio of the inorganiccarbonate to substituted phthalic compound in a range from about 1.0moles to about 1.5 moles of inorganic carbonate to about 1 mole ofsubstituted phthalic compound (VI).

In one embodiment, the first product mixture, obtained as describedabove comprises at least 25 weight percent by weight of theoxybisphthalic compound. In another embodiment, the oxybisphthaliccompound is present in the first product mixture in an amountcorresponding to at least 35 percent by weight of a total weight of thefirst mixture. In yet another embodiment, the oxybisphthalic compound ispresent in the first product mixture in an amount corresponding to atleast 50 percent by weight of a total weight of the first mixture.Typically, the first product mixture is a slurry in which a portion ofthe oxybisphthalic compound is dissolved in the solvent and a portion ofthe oxybisphthalic compound is present as a solid phase of the slurry.Owing to their generally poor solubility, the alkali metal halides andalkaline earth metal halides typically remain as solids within the firstmixture. It will be understood by those skilled in the art that the word“mixture” as used herein refers to a combination of at least twocomponents at least one of which is at least partially insoluble in theother. Thus each of the “first product mixture”, the “second productmixture” and the “third product mixture” comprises at least onecomponent that is at least partially insoluble. For example, in oneembodiment, the “third product mixture” is a mixture in whichessentially all of the oxybisphthalic compound is in solution, but atleast a portion of the inorganic salt remains insoluble and is presentas a solid phase component of the mixture. Typically, the inorganic saltis highly insoluble in the “third product mixture” allowing separationof the inorganic and organic components of the mixture by filtering offthe inorganic salt.

The first product mixture is then diluted with at least one solvent toprovide a second product mixture wherein the oxybisphthalic compound ispresent in an amount corresponding to less than 25 percent by weight ofthe total weight of the second product mixture. In another embodiment,the oxybisphthalic compound is present in an amount corresponding toless than 15 percent by weight of the total weight of the second productmixture. In yet another embodiment, the oxybisphthalic compound ispresent in an amount corresponding to less than 10 percent by weight ofthe total weight of the second product mixture. In one embodiment, thesolvent employed in diluting the first product mixture isortho-dichlorobenzene. In alternate embodiments the solvent employed isat least one solvent selected from the group consisting ofchlorobenzene, para-dichlorobenzene, dichlorotoluene,1,2,4-trichlorobenzene, diphenyl sulfone, phenetole, anisole, veratrole,toluene, xylene, mesitylene, and mixtures thereof. In yet anotherembodiment, the solvent employed comprises ortho-dichlorobenzene and atleast one other aromatic solvent. Non-limiting examples of suitablearomatic solvents include toluene, mesitylene, xylene, etc.

In one embodiment of the present invention, essentially all of theoxybisphthalic anhydride present in the second product mixture isdissolved in the solvent to form a third product mixture (step (c)).Suitable solvents include those discussed herein, for example anisole,chlorobenzene, ortho-dichlorobenzene, etc. Typically, a single solventis employed in each of steps (a)-(e) for preparing an oxybisphthaliccompound. Ortho-dichlorobenzene is in certain instances a preferredsolvent. Typically the dissolution of the oxybisphthalic anhydride (step(c)) is effected by heating the second product mixture to a temperaturein the range from about 80° C. to about 220° C. in an embodiment, fromabout 100° C. to about 200° C. in another embodiment, and from about130° C. to about 180° C. in still another embodiment. Upon dissolutionof essentially all of the oxybisphthalic anhydride the “third productmixture” is formed. Typically, this third product mixture comprises lessthan 25 ppm of water. In one embodiment, the third product mixturecomprises less than 15 ppm of water. In yet another embodiment, thethird product mixture comprises less than 5 ppm of water. It is believedthat it is generally preferable that the third product mixture containas little water as possible. The presence of water in any of the stepsused for preparing the oxybisphthalic compound is thought to contributeto water in the final oxybisphthalic compound product. Higherconcentrations of water are thought to be the source of higher thandesired levels of alkali metal ions in the product oxybisphthalicanhydride. In one embodiment, distillation of a portion of the solventpresent in the third product mixture aids in removal of some of thewater, thereby leading to the formation of a more concentrated thirdproduct mixture comprising less than 25 ppm water.

Next, the third product mixture is filtered to separate the insolubleinorganic salt from the dissolved oxybisphthalic compound. Thefiltration is carried out at a temperature above the crystallizationpoint temperature of the oxybisphthalic compound in order to avoidcrystallization within the device used to effect the filtration. As willbe understood by those skilled in the art, the crystallization pointtemperature is a function of a number of parameters including theconcentration of the dissolved oxybisphthalic compound in the solvent,the properties of the solvent, the structure of the oxybisphthaliccompound, and the state of purity of the oxybisphthalic compound (e.g.,mixtures of isomeric oxybisphthalic anhydrides versus single isomeroxybisphthalic anhydrides). The crystallization point temperature istypically in a range from about 0° C. to about 200° C. Typically, thefiltration device is a porous filter that can be heated to maintain atemperature above the crystallization point temperature of theoxybisphthalic compound. In an embodiment, the filtration step yields a“first solution”, that is a homogenous solution containing theoxybisphthalic compound, and a filter cake, the filter cake beingcomprised of the solid components of the third product mixture. Thefilter cake typically contains the inorganic salt as the major componenttogether with a lesser amount of the oxybisphthalic compound. In anembodiment, from about 5 to about 10 weight percent of the total amountof oxybisphthalic compound present initially in the first productmixture forms part of the filter cake. In one embodiment the filteringis carried out at a temperature in a range from about 50° C. to about250° C., in another embodiment from about 100° C. to about 225° C., andin yet another embodiment from about 125° C. to about 190° C. Typically,the filtering is carried out at (0 PSIG), near (5-25 PSIG) atmosphericpressure, or super-atmospheric pressure (for example at 25-100 PSIG)under an inert atmosphere, for example under a nitrogen atmosphere. Asub-atmospheric vacuum driving force filtration can also be carried outto effect separation of the solution and solids. Filtering may becarried out employing methods known in the art. In one embodiment, thefiltering is carried out in a metal filter. In an alternate embodiment,the filtering is carried out in a ceramic filter. In one embodiment, thefilter is a sintered metal filter having a pore size in a range fromabout 0.5 microns to about 5 microns. In various embodiments of thepresent invention, the filter employed has a pore size in a range fromabout 0.1 microns to about 10 microns, alternately from about 0.2microns to about 5 microns.

The first solution comprises the oxybisphthalic compound, the organicphase transfer catalyst, and other impurities dissolved in an organicsolvent. For example, when 4,4′-ODPA is produced from theHEGCl-catalyzed reaction of 4-chlorophthalic anhydride and potassiumcarbonate in ODCB, a significant amount of HEGCl, HEGCldegradation/reaction products, and amine color bodies are present in thefirst solution and remain in the 4,4′-ODPA product after crystallizationfrom the first (ODCB) solution. Typically, the first solution comprisesthe organic phase transfer catalyst in an amount corresponding to fromabout 500 ppm to about 5000 ppm in an embodiment, from about 1000 ppm toabout 3000 ppm in another embodiment, and from about 1000 ppm to about2000 ppm in still another embodiment. Various techniques, such as ionchromatography (IC), high pressure liquid chromatography (HPLC), andnuclear magnetic resonance (NMR) spectroscopy can be used toquantitatively measure the amount of the organic phase transfercatalyst.

In accordance with an aspect of the present invention, the firstsolution is contacted with a solid inorganic adsorbent material toprovide a second solution of the oxybisphthalic compound I, which issubstantially free of the organic phase transfer catalyst. Thecontacting step may be carried out either in a continuous or abatch-wise manner. The term “contacting” herein refers to anycombination of heating and stirring, or heating and flowing through apacked bed of a solid adsorbent. Thus in an embodiment, “contacting”comprises heating without stirring, in another embodiment, it refers toheating with stirring. Stirring with heating is generally preferredsince it facilitates good contact of the surfaces of the adsorbentmaterial with the organic phase transfer catalyst present in thesolution phase. In another embodiment, the solution is passed through asingle bed packed with solid adsorbent in batch mode, or through aseries of packed beds to simulate counter-current “contacting” ofsolution and adsorbent. A variety of solid inorganic adsorbent materialscan be used. The adsorption capacity of a solid inorganic adsorbentmaterial depends upon, among other factors, the pore size (or porediameter) and the cumulative pore volume distribution of the adsorbentparticles. Pore size measurements can be made using any of the methodsknown in the art. Cumulative pore volume distribution can be obtainedfrom the total cumulative pore volume, which in turn can be obtainedfrom the total pore volume. Total pore volume is given by the sum ofpore volumes of all adsorbent particles over the entire pore size rangepresent in the adsorbent sample. Total cumulative pore volume for agiven pore size (such as for example, particles having a pore size ofless than about 3 nanometers, less than about 10 nanometers, less thanabout 20 nanometers, and the like) is expressed as a percentage of thetotal pore volume. The cumulative pore volume distribution for a givenpore size or pore size range (such as for example, less than about 3nanometers, from about 3 nanometers to about 10 nanometers, from about 3nanometers to about 20 nanometers, and the like) in turn can be obtainedfrom the total cumulative pore volume. Adsorbent materials that providea mesoporous surface or a combination of mesoporous and microporoussurfaces can be used. Microporous adsorbent materials have a pore size(hereinafter also expressed as “pore diameter”) of less than about 3nanometers. In another embodiment, adsorbent materials having a poresize of less than about 10 nanometers can be used. Mesoporous adsorbentmaterials having a pore size of less than 60 nanometers in anembodiment, in a range between about 10 nanometers and about 20nanometers in another embodiment, and in a range between about 3nanometers and 20 nanometers in still another embodiment, can also beused. Exemplary adsorbent materials include silica, alumina, zeolites,inorganic ion exchange compounds, and mixtures thereof. Some examples ofinorganic ion exchangers include the aluminophosphate andaluminosilicate class of materials. Silica-based adsorbents arepreferred since they generally have a higher capacity and selectivityfor adsorbing the organic phase transfer catalyst. Silica adsorbents arefound to have a more uniform pore size (or a narrower pore sizedistribution). Commercially available silica adsorbent materials areavailable which are sufficiently robust so that the pore structure ofthe silica will not collapse or degenerate when contacted with a polarmedium such as water. In a preferred embodiment, the present inventionemploys a silica which is resistant to pore collapse when in contactwith water during a regeneration step. Examples of suitable adsorbentsinclude those available commercially from PQ Corporation, such as theC930 and R100 silicas; and CBV901 zeolite. It is typically preferable todry the adsorbents prior to contacting the first solution with a solidinorganic adsorbent material. Drying of the solid inorganic adsorbentmaterial can be accomplished by heating at temperatures between 150° C.to about 250° C. under vacuum. Adsorbent materials dried in this mannerhave significantly higher adsorption capacity for impurities such as theorganic phase transfer catalyst, amine color bodies, and otherimpurities; and also a higher selectivity for adsorbing the phasetransfer catalyst than the oxybisphthalic compound.

As noted, typically the contacting of the adsorbent material and thefirst solution is carried out at a temperature in a range between about50° C. and about 250° C. in an embodiment, between about 80° C. andabout 200° C. in another embodiment, and between about 100° C. and 160°C. in yet another embodiment. The organic phase transfer catalyst levelin the first solution generally ranges from about 500 ppm to about 5000ppm in an embodiment, from about 1000 ppm to about 3000 ppm in anotherembodiment, and from about 1000 ppm to about 2000 ppm in still anotherembodiment. In a further embodiment, the first solution contains theorganic phase transfer catalyst at a level equal to that used in thereaction to form the oxybisphthalic compound, and can range from5000-25000 parts per million. The first solution generally comprisesless than or equal to about 25 weight percent of the oxybisphthaliccompound. When an ODPA solution in ODCB is used, for example, thesolution may comprise, in various embodiments, about 1 to about 25weight percent, about 5 to about 15 weight percent, or about 5 to about10 weight percent of ODPA.

In accordance with another aspect of the present invention, removal oforganic phase transfer catalyst from the oxybisphthalic compound canalso be accomplished by contacting a dry or a wet cake sample of theoxybisphthalic compound with a slurry of the solid inorganic adsorbentmaterial in a suitable solvent. In this approach, the solid inorganicadsorbent material is first suspended in at least one solvent (e.g.,ODCB) to give a slurry. The adsorbent is then allowed to equilibratewith the solvent. Equilibration of the adsorbent material is achieved bymaintaining the contact of the solid inorganic adsorbent material withthe solvent for about 1 hour in an embodiment, and for about 2 hours inanother embodiment. Dry or wet oxybisphthalic compound (wet due topresence of residual organic solvent in the product from the reactionforming the oxybisphthalic compound) is then added to the slurry of thesolid inorganic adsorbent material in the solvent and the resultantmixture is then allowed to equilibrate for a longer or shorter period arequired. Typical equilibration times may range from less than a minuteto several hours. In one embodiment, equilibration of the mixture of thefirst solution and the solid inorganic adsorbent material is carried outfor 1 hour. In an alternate embodiment, a 2 hour equilibration period isused. In yet another embodiment, a 3 hours equilibration period is used.During the period of contact between the first solution and the solidinorganic adsorbent material, the organic phase transfer catalyst isadsorbed onto the solid inorganic adsorbent material, thereby reducingthe level of dissolved phase transfer catalyst. The slurry prepared fromthe first solution and the solid inorganic adsorbent material is thenfiltered to furnish purified oxybisphthalic compound as a “secondsolution”, from which the oxybisphthalic compound may be crystallized.

In one embodiment, the present invention provides a second solution ofan oxybisphthalic compound having structure I, which is substantiallyfree of organic phase transfer catalyst. Those skilled in the art willappreciate that crystallization of the oxybisphthalic compound from asecond solution which is substantially free of organic phase transfercatalyst will result in a solid oxybisphthalic compound which is alsosubstantially free of organic phase transfer catalyst. In oneembodiment, crystallization of the oxybisphthalic compound from a secondsolution which is substantially free of organic phase transfer catalystresults in a slurry comprising the solid oxybisphthalic compound and asolvent, said slurry being substantially free of organic phase transfercatalyst. As used herein, the expression “substantially free of” meansthat the residual amount of organic phase transfer catalyst present isless than about 150 ppm. A second solution which is substantially freeof organic phase transfer catalyst comprises less than about 150 ppmorganic phase transfer catalyst. By way of further illustrating themeaning of “substantially free of organic phase transfer catalyst” asused herein, an oxybisphthalic compound (I) which is substantially freeof organic phase transfer catalyst comprises less than about 150 ppmorganic phase transfer catalyst; and an oxybisphthalic anhydride (IV)which is substantially free of organic phase transfer catalyst comprisesless than about 150 ppm organic phase transfer catalyst.

In one embodiment, the present invention provides a purifiedoxybisphthalic compound having structure (I), wherein the purifiedoxybisphthalic compound is substantially free of organic phase transfercatalyst. In one embodiment, the present invention provides a purifiedoxybisphthalic compound (I) comprising less than about 150 ppm of theorganic phase transfer catalyst. In an alternate embodiment, the presentinvention provides a purified oxybisphthalic compound (I) comprisingfrom about 2 parts per million (ppm) to about 120 ppm of the organicphase transfer catalyst. In yet another embodiment, the presentinvention provides a purified oxybisphthalic compound (I) comprisingfrom about 5 ppm to about 100 ppm of the organic phase transfercatalyst.

In one embodiment, the present invention provides a purifiedoxybisphthalimide having structure (II), wherein the purifiedoxybisphthalimide is substantially free of organic phase transfercatalyst. In one embodiment, the present invention provides a purifiedoxybisphthalimide (II) comprising less than about 150 ppm of the organicphase transfer catalyst. In an alternate embodiment, the presentinvention provides a purified oxybisphthalimide (II) comprising fromabout 2 parts per million (ppm) to about 120 ppm of the organic phasetransfer catalyst. In yet another embodiment, the present inventionprovides a purified oxybisphthalimide (II) comprising from about 5 ppmto about 100 ppm of the organic phase transfer catalyst.

In one embodiment, the present invention provides a purifiedoxybisphthalic anhydride having structure (IV), wherein the purifiedoxybisphthalic anhydride is substantially free of organic phase transfercatalyst. In one embodiment, the present invention provides a purifiedoxybisphthalic anhydride (IV) comprising less than about 150 ppm of theorganic phase transfer catalyst. In an alternate embodiment, the presentinvention provides a purified oxybisphthalic anhydride (IV) comprisingfrom about 2 parts per million (ppm) to about 120 ppm of the organicphase transfer catalyst. In yet another embodiment, the presentinvention provides a purified oxybisphthalic anhydride (IV) comprisingfrom about 5 ppm to about 100 ppm of the organic phase transfercatalyst.

After the adsorptive removal of organic phase transfer catalyst andother impurities by the solid adsorbent material, the adsorbent materialmay become “spent”, i.e., it may not be able to adsorb any more, or apractically useful level of the organic phase transfer catalystimpurity. The spent adsorbent may be regenerated for reuse in theadsorption process. Regeneration can be accomplished by desorbing theorganic phase transfer catalyst and the co-adsorbed oxybisphthaliccompound using a polar liquid medium, such as water, preferably hotwater; steam, methanol, ethanol, isopropanol, aliphatic and/or aromaticalcohols, aqueous acids, such as aqueous phosphoric acid, and the like.Hot water in the range of 40° C. to 100° C., or more preferably from 80°C. to 100° C. can be used. In another embodiment, superheated water attemperatures greater than 100° C. under pressure can be used. In otherembodiments, the adsorbent may be regenerated with hot oxidizing gasessuch as air, oxygen, or carbon dioxide; with acids such as hydrochloricacid or sulfuric acid in temperature ranges from 100° C. to 300° C.,preferably from 150° C. to 250° C., at atmospheric or elevatedpressures. In a still another embodiment, the adsorbent can beregenerated using a supercritical gas, such as carbon dioxide.

As noted, the product oxybisphthalic compound may be further purified bycrystallization from the second solution. Typically the crystallizationis effected using conventional techniques that are well known in the artat a temperature corresponding to the crystallization point temperatureor a lower temperature. Thus, crystallization of the oxybisphthaliccompound from the homogenous second solution is typically effected at atemperature in a range from about 0° C. to about 200° C. In oneembodiment, the crystallization is effected at a temperature in a rangeof from about 10° C. to about 120° C. In an alternate embodiment,crystallization is effected at a temperature in a range from about 10°C. to about 80° C. Typically, the crystallization is effected in avessel equipped with an agitator. When the crystallization step iseffected under agitation, the product of the crystallization step is aslurry of the crystallized oxybisphthalic compound in the solvent.Crystallized oxybisphthalic compound obtained in this manner typicallycomprises residual organic phase transfer catalyst. In one embodiment,the crystallized oxybisphthalic compound comprises less than about 100ppm of the organic phase transfer catalyst. In an alternate embodiment,the crystallized oxybisphthalic compound comprises residual organicphase transfer catalyst in an amount corresponding to from about 1 ppmto about 90 ppm. In yet another embodiment, the crystallizedoxybisphthalic compound comprises residual organic phase transfercatalyst in an amount corresponding to from about 1 ppm to about 10 ppm.

Those skilled in the art will understand that the purifiedoxybisphthalimides (I) may be converted into oxybisphthalic anhydrideshaving structure (IV) by hydrolysis to the corresponding tetraacidfollowed by ring closure to the dianhydride. Hydrolysis of theoxybisphthalimide (I) may be effected by various means, for example byheating the oxybisphthalimide (I) in aqueous sodium hydroxide. Thehydrolysis product, a tetra sodium carboxylate, may be neutralized witha strong acid, for example hydrochloric acid, to produce thecorresponding tetraacid which precipitates from solution. The tetraacidintermediate may be isolated, for example by filtration, and thereaftersubjected to ring closure of the tetraacid to the correspondingdianhydride. In one embodiment, ring closure of the tetraacid to thecorresponding dianhydride is effected by heating the tetraacid to atemperature above its melting point and driving off water.

The oxybisphthalic anhydrides purified by the method of the instantinvention are valuable for preparing polyetherimides. In one aspect thenthe present invention provides a method comprising combining at leastone solvent, at least one purified oxybisphthalic anhydride, and atleast one diamino aromatic compound to form a polymerization mixtureunder art-recognized conditions suitable for the condensationpolymerization of an oxybisphthalic anhydride with an aromatic diamine.Typically, such conditions involve heating a solution of roughly equalmolar amounts of the oxybisphthalic anhydride and diamine in thepresence of an imidization catalyst such as sodium phenylphosphinate(SPP, C₆H₅PO₂Na). The polymerization reaction is generally conductedunder conditions such that the solvent is continuously refluxing. A trapsuch as a Dean-Stark trap may be employed to separate water formedduring the condensation polymerization. In general, the polymerizationreaction is most efficient and higher molecular weight polyetherimideproduct is obtained when as much water as possible is removed from thereaction mixture.

In one embodiment, the at least one diamino aromatic compound may berepresented by formula (XII)H₂N—B—NH₂  (XII)wherein B is a C₃-C₃₀ divalent aromatic radical. In one embodiment B isa monocyclic divalent aromatic radical, for example praraphenylene,metaphenylene, or combinations thereof. In an alternate embodiment B isa polycyclic divalent aromatic radical, for example 4,4′-biphenylene or1,4-naphthalene.

In one embodiment B is a C₃-C₃₀ divalent aromatic radical havingstructure (XIII)

wherein the unassigned positional isomer about the aromatic ring iseither ortho, meta or para to Q, and Q is a linking group chosen from

a covalent bond, an alkylene group of the formula C_(y)H_(2y), or analkylidene group of the formula C_(y)H_(2y); wherein “y” is an integerfrom 1 to 5 inclusive. In some particular embodiments “y” has a value ofone or two. Illustrative alkylene and alkylidene linking groups Qinclude, but are not limited to, methylene, ethylene, ethylidene,propylene, and isopropylidene. In other particular embodiments theunassigned positional isomer about the aromatic ring in formula (XIII)is para to Q.

In certain embodiments, the two amino groups present in diamino aromaticcompound XII are separated by at least two and sometimes by at leastthree ring carbon atoms. For example, the amino groups present inmeta-phenylene diamine are separated by three ring carbon atoms. By wayof further example, the amino groups present in para-phenylene diamineare separated by four ring carbon atoms. When the amino group or groupsare located in different aromatic rings of a polycyclic aromatic moietycomprising structure (XIII), they are often separated from the linkinggroup Q between by at least three ring carbon atoms.

Diamino aromatic compounds XII are illustrated by2-methyl-1,3-diaminobenzene; 4-methyl-1,3-diaminobenzene;2,4,6-trimethyl-1,3-diaminobenzene; 2,5-dimethyl-1,4-diaminobenzene;2,3,5,6-tetramethyl-1,4-diaminobenzene;1,2-bis(4-aminoanilino)cyclobutene-3,4-dione,bis(4-aminophenyl)-2,2-propane;bis(2-chloro-4-amino-3,5-diethylphenyl)methane, 4,4′-diaminodiphenyl,3,4′-diaminodiphenyl, 3,3′-diaminodiphenyl,3,3′-dimethyl-4,4′-diaminodiphenyl, 3,3′-dimethoxy-4,4′-diaminodiphenyl,2,2′,6,6′-tetramethyl-4,4′-diaminobiphenyl;3,3′-dimethoxy-4,4′-diaminobiphenyl; 4,4′-diaminodiphenylmethane,3,3′-diaminodiphenylmethane, 3,4′-diaminodiphenylmethane,1,3-bis(3-aminophenoxy)benzene, 1,3-bis(4-aminophenoxy)benzene,1,4-bis(4-aminophenoxybenzene), bis(4-(4-aminophenoxy)phenyl)sulfone,bis(4-(3-aminophenoxy)phenyl)sulfone,4-(4-aminophenoxy)phenyl)(4-(3-aminophenoxy)phenyl)sulfone,4,4′-bis(3-aminophenoxy)biphenyl, 4,4′-bis(4-aminophenoxy)biphenyl,4-(3-aminophenoxy)-4′-(4-aminophenoxy)biphenyl,2,2′-bis(4-(4-aminophenoxy)phenyl)propane,2,2-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane,4,4′-bis(aminophenyl)hexafluoropropane, 4,4′-diaminodiphenyl ether,3,4′-diaminodiphenyl ether, 3,3′-diaminodiphenyl ether,4,4′-diaminodiphenylsulfide, 3,4′-diaminodiphenylsulfide,3,3′-diaminodiphenylsulfide, 3,3′-diaminodiphenylsulfone,4,4′-diaminodiphenyl sulfone, 3,4′-diaminodiphenyl sulfone,4,4′-(9-fluorenylidene)dianiline; 4,4′-diaminodiphenyl ketone,3,4′-diaminodiphenyl ketone, 3,3′-diaminodiphenyl ketone,2,6-diaminotoluene and 2,4-diaminotoluene.

In one embodiment, two or more diamino aromatic compounds can also beused. For example, the ETHACURE diamines, available from AlbemarleCorporation, Baton Rouge, La., such as ETHACURE 100, which is a 80:20weight ratio combination of 2,6-diethyl-4-methyl-1,3-phenylene diamineand 4,6-diethyl-2-methyl-1,3-phenylene diamine, respectively; andETHACURE 300 which is a 80:20 weight ratio combination of2,6-bis(mercaptomethyl)-4-methyl-1,3-phenylenediamine and4,6-bis(mercaptomethyl)-2-methyl-1,3-phenylene diamine, respectively,can also be used. Perfluorinated alkyl or partially fluorinated alkylanalogs of said diamines are also suitable for use.

EXAMPLES

The following examples are set forth to provide those of ordinary skillin the art with a detailed description of how the methods claimed hereinare evaluated, and are not intended to limit the scope of what theinventors regard as their invention.

Reagent grade ODCB was used for all experimental studies, and was driedto specific water levels by distillation at reflux conditions. Waterlevels in the ODCB were measured by Karl Fischer analysis using 500microliters of distilled ODCB samples.

Adsorbents were received from the manufacturer and dried to constantweight in a vacuum oven maintained at 160° C. and reduced pressure (380mm Hg). Silica samples were dried by suspending them in ODCB anddistilling out the ODCB to facilitate removal of water.

A low temperature nitrogen adsorption technique was used to probe theadsorbent surface. By employing the Brunauer-Emmett-Teller (BET)equation for isotherms, which depend on the partial pressure and vaporpressure of the adsorbate, and the Barret-Joyner-Halenda (BJH) methodfor pore size analysis, the pore volume and pore surface area, as afunction of pore diameter (pore size) was developed. Using the BJHmethod in conjunction with the BET adsorption and desorption isothermsat −196° C. (77° K.) for nitrogen on the adsorbent, a pore sizedistribution for the adsorbent was determined.

Oxydiphthalic anhydride (ODPA) samples containing HEGCl phase transfercatalyst were received as wet solids due to the presence of ODCB in thesamples. The samples were dried to constant weight in a vacuum ovenmaintained at 160° C. and reduced pressure (380 mm Hg). HEGCl levelswere measured by an HPLC technique using an Agilent Zorbax SB-C-184.6×75 mm 3.5μ HPLC column that was maintained at 25° C. A 0.1 gramsample of dry ODPA was taken in a vial and treated with 5 milliliters ofa solution of acetonitrile containing 0.288 milligram of phenanthrene(internal standard). The mixture was heated to about 90° C. for 1-3minutes to obtain a homogeneous solution, which was filtered. A4-microliter sample of the filtrate was used for the HPLC analysis.Aqueous H₃PO₄ was prepared by taking 3 milliliters of concentrated H₃PO₄(85% H₃PO₄ in water) and diluting to 3800 milliliters total volume usingdeionized water.

TABLE 1 Elution CH₃CN Methanol Time Flow (volume Aqueous H₃PO₄ (volume(min) (ml/min) percent) (volume percent) percent) 0 1.5 40 59 1 10 1.540 59 1 14 1.5 90 0 10 16 1.5 40 59 1 20 1.5 40 59 1

Example 1

This Example describes the general procedure used for batch adsorptionexperiments using C-930 silica (available from PQ Corporation) as theadsorbent material.

The required amounts of ODPA containing a known amount of HEGCl andpre-dried silica samples were weighed out separately so as to achieve adesired ODPA/silica weight ratio. The silica sample was added topre-dried ODCB solvent to provide approximately a 5 weight percentslurry. The slurry was heated and maintained at a constant temperatureof 140° C., 150° C., or 160° C. with stirring for 1-2 hours to allow fortemperature equilibration prior to adding ODPA. To this slurry was addedthe ODPA as a dry solid. When all the ODCB had dissolved, the resultingslurry of silica in ODPA/ODCB solution was equilibrated for 3 hours bystirring at the desired temperature, 140° C., 150° C., or 160° C. Theslurry was hot filtered using a 0.5-micron sintered metal filter heatedto about 170° C. This removed the adsorbent from the ODPA solution. Tomaximize the recovery of purified ODPA, the filter cake was washed withhot ODCB at 160° C. to remove any ODPA present in the adsorbent filtercake. The filtrate was then cooled and crystallized while mixing. Theresulting ODPA crystals were isolated from the slurry on a Buchnerfunnel using filter paper. The filter cake was washed with ODCB todisplace mother liquor remaining in the ODPA wet cake. The washed filtercake was then dried to constant weight in a vacuum oven maintained at160° C. and reduced pressure (380 mm Hg). The mother liquor was analyzedfor HEGCl and residual ODPA. Residual HEGCl content in the dried ODPAwas also measured. Material balances with respect to ODPA and HEGCl weregenerally greater than 95 weight percent. Results from the adsorptivepurification experiments are shown in Table 2.

TABLE 2 HEGCl HEGCl adsorbed by Isolated yield Moisture HEGCl in silica(weight of purified in silica in feed purified percent of ODPA ExampleODPA/Silica adsorbent ODPA ODPA initial HEGCl (weight Number weightratio (ppm) (ppm) (ppm) level) percent) 2 7.3 10 1126 90 87 97 3 3.8 101446 44 94 95 4 4 40 1237 9 98 93 5 2 10 1335 10 99 85 6 4 10 1236 4 9992 7 4 10 1399 40  97*  93* 8 1.3 10 1335 4 >99   79 Indicates that thesilica adsorbent obtained from the 1^(st) treatment cycle wasregenerated and used for a second batch purification of ODPA.

The results in Table 2 show that pre-dried silica is effective inremoving HEGCl from ODPA prepared using HEGCl as a phase transfercatalyst.

The procedure of Example 1 was used with C-930 Silica and otheradsorbents, such as R-100 Silica, CBV901 zeolite, BG-HHM Carbon, CalgonRB Carbon, and Calgon BL Carbon. Table 3 shows the HEGCl adsorptioncapacity (milligrams per gram), total pore volume (milliliters pergram), and cumulative pore volume distribution, which is expressed as apercent of the total pore volume, and as a function of the pore diameterrange (expressed in nanometers) of the adsorbent particles. The resultsshow that silica and zeolite adsorbents which have a total pore volumeof 0.5 milliliters/gram or greater, and a cumulative pore volumedistribution of about 20 percent or greater of particles having a porediameter in a range between about 3 nanometers and about 20 nanometersare more effective in adsorbing HEGCl from a solution of ODPA.

TABLE 3 Total Cumulative pore volume distribution (%, as a function ofpore Example HEGCl Total pore surface diameter range of adsorbentparticles) Number Adsorbent Capacity volume area <3 nm 3-10 nm 10-20 nm20-30 nm 30-60 nm >60 nm 9 C-930 Silica 124.4 1.42 453 10.6 45.2 41.41.1 0.7 1 10 R-100 Silica 91.5 0.55 277 7 37.8 48.1 3.4 2.1 1.5 11CBV901 Zeolite 21.9 0.5 676 55.7 10.7 8.5 5.5 13.9 5.3 12 Calgon RBCarbon 0.4 0.85 1343 68.2 15.4 6.2 2.5 4.6 2.9 13 Calgon BL Carbon 0.30.59 1005 73 13.2 5.7 2 3.8 1.8

Examples 14-17

Examples 14-17 illustrate regeneration of “spent” solid inorganicadsorbent material. The procedures are illustrated for Silica C-930adsorbent that contained HEGCl and ODPA. The “Spent” Silica C-930 wasboiled in an excess of water, 2-propanol, water containing 4 weightpercent of phosphoric acid, or ODCB (maintained at 170° C.) for 2 hours.In each case, the slurry was filtered and the amount of HEGCl and ODPApresent in the filtrate was measured. Then the amount of HEGCl desorbedfrom the silica was calculated. The data is shown in table 4. “NA”stands for “not applicable.” The data shows that all the solvents arecapable of desorbing HEGCl and ODPA from the silica, however, water andaqueous phosphoric acid are relatively more effective.

TABLE 4 Wt % HEGCl/ODPA Mass Desorbed Example Regeneration T loadedsilica (wt % of Number Solution (° C.) in solvent pH initial) 14 ODCB170 19.75 NA 5.7 15 H₃PO₄/H₂O 100 8.51 1.3 26.2 16 H₂O 100 9.14 6.0 27.417 2-propanol 82 8.93 ~7 10.1

Thermo-gravimetric analysis (TGA) was carried out to determine theamount of HEGCl and ODPA adsorbed on the “spent” C-930 silica sample.The sample was heated from an initial temperature of 20° C. to 800° C.in air to thermally desorb the HEGCl and ODPA from the silica surface.The above procedure was also repeated with a clean sample of commercialsilica C-930 sample and used as a blank.

Example 18 Preparation of Polyetherimide from Purified 4,4′-ODPA

A 1-liter glass reactor equipped with a mechanical agitator and anoverhead condenser system adapted for removing a distillate was chargedwith 1,2-dichlorobenzene (565 grams), 4,4′-ODPA (purified by treating4,4′-ODPA having 1086 ppm HEGCl with C-930 silica to a purified4,4′-ODPA having 6 ppm of HEGCl, 74.6 grams), bisphenol A dianhydride(6.5 grams), meta-phenylene diamine (18.2 grams), para-phenylene diamine(7.8 grams), and aniline (1.8 grams). The reactor flask was immersed ina hot oil bath and the contents of the reactor were heated with stirringto a temperature of 180° C. to 190° C. 1,2-ODCB solvent and water fromimidization were collected as a distillate over a period of about 12hours. No stoichiometric adjustments of the various reactants wereneeded. After the reaction flask was cooled, the polymer was isolated byfiltration and oven-dried. The final polymer material had 0.21 molepercent of net anhydride functional groups.

While only certain features of the invention have been illustrated anddescribed herein, many modifications and changes will occur to thoseskilled in the art. It is, therefore, to be understood that the appendedclaims are intended to cover all such modifications and changes as fallwithin the true spirit of the invention.

What is claimed is:
 1. A method of purifying a dianhydride, said methodcomprising the steps of: a. providing a first solution comprising atleast one dianhydride, at least one solvent, and at least one organicphase transfer catalyst; and b. contacting the first solution with asolid inorganic adsorbent material, said solid inorganic adsorbentmaterial having a total pore volume of about 0.5 milliliters/gram orgreater, and a cumulative pore volume distribution of about 20 percentor greater of particles having a pore diameter in a range between about3 nanometers and about 20 nanometers; to provide a second solution ofthe dianhydride, which is substantially free of the organic phasetransfer catalyst, wherein the solid inorganic adsorbent material isselected from the group consisting of silica, alumina, zeolites,inorganic ion exchange compounds and mixtures thereof.
 2. The method ofclaim 1, wherein the phase transfer catalyst is selected from the groupconsisting of hexaalkylguanadinium salts, pyridinium salts, andphosphazenium salts.
 3. The method of claim 1, wherein the phasetransfer catalyst is a bisguanadinium salt.
 4. The method of claim 1wherein the adsorbent is a silica-based adsorbent.